In conventional machines for manufacturing corrugated paperboard boxes, flat rectangular corrugated paperboard blanks advance in a horizontal machine direction through a printer-cutter machine, which performs diverse printing and cutting operations. The thickness of the paperboard blanks typically varies from approximately 1/16 to 3/8 inch (0.16 to 0.95 cm). The blanks are initially stacked onto a feed mechanism, which is typically integral with the feed/print section of printer-cutter machine. The feed mechanism feeds the blanks one-by-one into the feed nip of the feed/print section of the printer-cutter machine. The feed mechanism, such as that described in Sardella, U.S. Pat. No. 4,614,335, feeds the box blanks from the bottom of the stack to the nip of feed rolls. The blanks are accelerated to the machine speed of the feed rolls by the feed mechanism, which feeds the blanks in a precise, fixed, synchronized relationship with the rotating print and cutting rolls so that the leading edge of the each blank is fed to the feed roll nip for exactly one revolution of the print and cutting rolls. This allows the print and cutting rolls to be precisely positioned relative to the leading edge of each blank.
The feed rolls transport the blanks to the nip between the print roll and an impression roll. One or more printing plates attached to the print roll print an image onto the blank. The position of the printed image is precisely set relative to the leading edge of the blank. The blank next enters the nip between a pair of pull rolls that transport the blank to the nip between the cutting roll and an anvil roll. A cutting die or knives attached to the cutting roll cut the blank. Again, the position of the die cut is precisely set relative to the leading edge of the blank. The cutting roll feeds the blank out of the machine, completing the operation of the printer-cutter machine.
Other arrangements of these basic operations are sometimes provided. For example, the machine might utilize two printing rolls for two-color printing, provide additional pull rolls, or provide the ability to slot and score the blank using additional sets of slotting and scoring rolls. For each of these operations, the blank is fed between two rotating rolls and the position of the desired image or impression is precisely set relative to the leading edge of the blank.
In order to provide access to adjust the machine for changes in the width of the blank, and also to allow the printing plates and cutting dies to be changed, the printer-cutter machine is divided into sections in the machine direction. These sections are locked together during operation, but may be separated when the machine is idle to provide an operator with access to the interior of the machine for conducting maintenance, changing the printing plates and cutting dies, and making other adjustments during machine setup. Although a complex machine may include several machine sections, even a basic machine includes at least two main sections--a feed/print section and a cutting section.
The power source for a printer-cutter machine is usually a direct-current main drive motor, generally about 40 horsepower. The main drive motor drives the lower feed roll through a V-belt drive, which drives a sheave. The opposite end of the feed roll is fitted with a spur-type gear that acts as the main driver for a gear-driven drive train that drives all of the machine rolls in a synchronized cyclic relationship, so that printing and cutting are synchronized to the leading edge of each blank. Power is transferred between machine sections through the gear mesh of the mating spur-type gears in the drive train at the line of separation between the machine sections. These spur-type gears between the machine sections come out of mesh when the sections are separate and go back into mesh when the sections are returned to the operating position.
The width of the nip between the upper and lower rolls of the printer-cutter machine are typically adjustable to accommodate changes in the thickness of the blank. When adjusting the nip, it is important to maintain the proper surface speed of the nip rolls to maintain constant machine speed without affecting the proper registration between the machine sections and the leading edge of the paperboard blank. In addition, the spur-type gears must not come out of mesh when the nip is adjusted.
Most conventional gear-driven printer-cutter machines use some form of an "Oldham coupling" for this purpose. With this type of coupling, the nip may be adjusted to accommodate changes in the thickness of the corrugated paperboard while the machine transmits power at a constant velocity and maintains a tight mesh between mating gears. In addition, the nip is adjusted without affecting the synchronized relationship of printing and cutting relative to the leading edge of the blank. In other words, the nip can be adjusted while maintaining constant machine speed and without affecting the proper registration between the machine sections and the leading edge of the paperboard blank.
Gear-driven corrugated paperboard printer-cutter machines using Oldham couplings work well in many respects, but suffer from a number of disadvantages:
(a) The cost of manufacturing a new machine is high because the spur-type gears must be custom designed, hardened, and manufactured in relatively small production quantities. PA1 (b) Backlash between mating gears increases with wear of the gear teeth. The backlash of each gear mesh is cumulative in the drive train, and thus tends to increase from the feeding mechanism, through the print roll, and to the cutting roll. Accordingly, the positional accuracy of the prints and cuts relative to the leading edge of the blanks, and relative to each other, deteriorates with the age of the gears of the drive train until the gears must be replaced. PA1 (c) The cost of replacing worn gears is high because the hardened spur-type gears must be custom designed and manufactured in small production quantities. Because many manufacturers stock only the parts used on their current production models, replacement parts for many machines are manufactured on an individual-machine basis, further increasing the cost of the replacement parts. As a result, a complete gear-train replacement for a typical printer-cutter machine can cost hundreds of thousands of dollars. PA1 (d) The Oldham couplings have oscillating components that must make one oscillation for each revolution of the coupled gear. The wear of these components exacerbates the gear-wear problem for conventional gear-driven printer-cutter machines. The additional backlash due to the wear of the Oldham coupling components is transferred to the associated driven roll. Accordingly, the positional accuracy of the prints and cuts relative to the leading edges of the blanks, and relative to each other, deteriorates with the age of the machine, until the Oldham coupling components must be replaced. PA1 (e) The cost of replacing worn Oldham couplings is high, for the same reasons listed above for drive train gears, and contribute to the high cost of a complete gear-train replacement. PA1 (f) Gear-driven drive trains and the associated Oldham couplings require lubrication and periodic oil changes. PA1 (g) Gear-driven drive trains and the associated Oldham couplings for printer-cutter machines are custom designed and cannot use lower cost, mass produced, standard stock gears and couplings that are available at competitive prices. PA1 (h) Gear-driven printer-cutter machines create high noise levels.
The S&S Corporation of Brooklyn, N.Y., manufactured gear-driven printer-cutter machines with stationary machine sections. Power was transmitted between machine sections by a stationary line shaft rigidly coupled to a stationary miter gearbox at each section. A spur-type gear mounted on the output of each miter gearbox provided the drive power for the gear-driven drive system for each machine section. The blanks were transported between the machine sections by a transfer assembly supported by the stationary machine sections. In the transfer assembly, the blanks were sandwiched between upper and lower synchronous belts to transport the blanks from one machine section to the next. Access to the machine sections for maintenance and setup was provided by a pit dug into the floor below the transfer assembly. This rather cumbersome design was abandoned about twenty years ago in favor of the conventional gear-driven Oldham coupling arrangement with separable machine sections described previously.
Accordingly, there is a need for a low-cost printer-cutter machine with separable machine sections that avoids the costs associated with a gear-driven drive train. There is a further need for a low-cost printer-cutter machine in which the nip between opposing rolls may be adjusted while maintaining constant machine speed and without affecting the proper registration between the machine sections and the leading edge of the paperboard blank.